1. Field of the Invention
The present invention relates to a light sensor and its manufacture method, and more particularly, to a light sensor and its manufacture method without using a CMOS process.
2. Description of Prior Art
More and more advanced-function displays have found their applications in current consumer electronic products. In particular, liquid crystal displays (LCDs) having a high-resolution color screen, are more widely applied in various electronic devices, such as televisions, mobile phones, personal digital assistances (PDA), digital cameras, desktop computer screens, and notebook computer screens.
To facilitate portability and usage of these devices, touch-control LCDs with an LCD touch panel to allow direct touch by the users have become the trend in the LCD market. Conventional resistor type or capacitor type LCD touch panels, which are configured by disposing additional resistors or capacitors on the panels, determine the coordinate positions of touch-points by detecting the voltage variation at the touch positions. However, since the resistors and capacitors are directly disposed on the panels, light transmittance through the LCD panel will be decreased and the overall thickness of the LCD panel will be increased. Another type of LCD touch panel, called an optical touch panel, is configured by disposing a large amount of light sources and corresponding optical detecting elements around an LCD panel. The coordinate position of a touch-point is determined when determining the position of an optical detecting element has failed to receive light rays from a corresponding light source. Although this design would not decrease the overall light transmittance through the panel, the product size is significantly increased. Accordingly, a touch-control LCD with detecting elements incorporated into a touch panel thereof is desirable to decrease the weight and volume of the LCD and thus meets the compact demand of the LCD market.
Referring to FIG. 1, which shows a conventional light sensor, the light sensor diode 10 is a P-I-N diode which contains a P-type area 12 doped with P-type dopants, an intrinsic layer 14 and an N-type area 16 doped with N-type dopants. The function of the intrinsic layer 14 is to increment a thickness of PN depletion region, so as to increase possibility of attracting photons and to reduce junction capacitor. The light sensor diode 10 induces electrical potential or photocurrent in accordance with incident light. When light is incident to the light sensor diode 10 and no bias voltage applied on the light sensor diode 10, electron-hole pairs are generated in the intrinsic layer 14 to increase a number of carriers, inducing photocurrent through the light sensor diode 10. When reverse bias voltage applied on the light sensor diode 10 (which means that the P-type area is coupled to a negative electrode of a power while the N-type is coupled to a positive electrode of the power), a reverse photoelectrical current is generated in proportion to luminance.
Traditionally, the intrinsic layer 14 is manufactured by poly-Si process. However, in contrast to amorphous silicon (a-Si) process, the intrinsic layer 14 manufactured by poly-Si has a lower sensitivity in sensing visible light. As a result, it is desirable to develop a new light sensor.